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/*
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 * Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  * Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
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 *  * Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
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 *  * Neither the name of JSR-310 nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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package java.time.chrono;

import static java.time.temporal.ChronoField.ERA;
import static java.time.temporal.ChronoUnit.ERAS;

import java.time.DateTimeException;
import java.time.temporal.UnsupportedTemporalTypeException;
import java.time.format.DateTimeFormatterBuilder;
import java.time.format.TextStyle;
import java.time.temporal.ChronoField;
import java.time.temporal.Temporal;
import java.time.temporal.TemporalAccessor;
import java.time.temporal.TemporalAdjuster;
import java.time.temporal.TemporalField;
import java.time.temporal.TemporalQueries;
import java.time.temporal.TemporalQuery;
import java.time.temporal.ValueRange;
import java.util.Locale;

/**
 * An era of the time-line.
 * <p>
 * Most calendar systems have a single epoch dividing the time-line into two eras.
 * However, some calendar systems, have multiple eras, such as one for the reign
 * of each leader.
 * In all cases, the era is conceptually the largest division of the time-line.
 * Each chronology defines the Era's that are known Eras and a
 * {@link Chronology#eras Chronology.eras} to get the valid eras.
 * <p>
 * For example, the Thai Buddhist calendar system divides time into two eras,
 * before and after a single date. By contrast, the Japanese calendar system
 * has one era for the reign of each Emperor.
 * <p>
 * Instances of {@code Era} may be compared using the {@code ==} operator.
 *
 * @implSpec This interface must be implemented with care to ensure other classes operate correctly.
 * All implementations must be singletons - final, immutable and thread-safe. It is recommended to
 * use an enum whenever possible.
 * @since 1.8
 */
public interface Era extends TemporalAccessor, TemporalAdjuster {

  /**
   * Gets the numeric value associated with the era as defined by the chronology.
   * Each chronology defines the predefined Eras and methods to list the Eras
   * of the chronology.
   * <p>
   * All fields, including eras, have an associated numeric value.
   * The meaning of the numeric value for era is determined by the chronology
   * according to these principles:
   * <ul>
   * <li>The era in use at the epoch 1970-01-01 (ISO) has the value 1.
   * <li>Later eras have sequentially higher values.
   * <li>Earlier eras have sequentially lower values, which may be negative.
   * </ul>
   *
   * @return the numeric era value
   */
  int getValue();

  //-----------------------------------------------------------------------

  /**
   * Checks if the specified field is supported.
   * <p>
   * This checks if this era can be queried for the specified field.
   * If false, then calling the {@link #range(TemporalField) range} and
   * {@link #get(TemporalField) get} methods will throw an exception.
   * <p>
   * If the field is a {@link ChronoField} then the query is implemented here.
   * The {@code ERA} field returns true.
   * All other {@code ChronoField} instances will return false.
   * <p>
   * If the field is not a {@code ChronoField}, then the result of this method
   * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)}
   * passing {@code this} as the argument.
   * Whether the field is supported is determined by the field.
   *
   * @param field the field to check, null returns false
   * @return true if the field is supported on this era, false if not
   */
  @Override
  default boolean isSupported(TemporalField field) {
    if (field instanceof ChronoField) {
      return field == ERA;
    }
    return field != null && field.isSupportedBy(this);
  }

  /**
   * Gets the range of valid values for the specified field.
   * <p>
   * The range object expresses the minimum and maximum valid values for a field.
   * This era is used to enhance the accuracy of the returned range.
   * If it is not possible to return the range, because the field is not supported
   * or for some other reason, an exception is thrown.
   * <p>
   * If the field is a {@link ChronoField} then the query is implemented here.
   * The {@code ERA} field returns the range.
   * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
   * <p>
   * If the field is not a {@code ChronoField}, then the result of this method
   * is obtained by invoking {@code TemporalField.rangeRefinedBy(TemporalAccessor)}
   * passing {@code this} as the argument.
   * Whether the range can be obtained is determined by the field.
   * <p>
   * The default implementation must return a range for {@code ERA} from
   * zero to one, suitable for two era calendar systems such as ISO.
   *
   * @param field the field to query the range for, not null
   * @return the range of valid values for the field, not null
   * @throws DateTimeException if the range for the field cannot be obtained
   * @throws UnsupportedTemporalTypeException if the unit is not supported
   */
  @Override  // override for Javadoc
  default ValueRange range(TemporalField field) {
    return TemporalAccessor.super.range(field);
  }

  /**
   * Gets the value of the specified field from this era as an {@code int}.
   * <p>
   * This queries this era for the value of the specified field.
   * The returned value will always be within the valid range of values for the field.
   * If it is not possible to return the value, because the field is not supported
   * or for some other reason, an exception is thrown.
   * <p>
   * If the field is a {@link ChronoField} then the query is implemented here.
   * The {@code ERA} field returns the value of the era.
   * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
   * <p>
   * If the field is not a {@code ChronoField}, then the result of this method
   * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
   * passing {@code this} as the argument. Whether the value can be obtained,
   * and what the value represents, is determined by the field.
   *
   * @param field the field to get, not null
   * @return the value for the field
   * @throws DateTimeException if a value for the field cannot be obtained or the value is outside
   * the range of valid values for the field
   * @throws UnsupportedTemporalTypeException if the field is not supported or the range of values
   * exceeds an {@code int}
   * @throws ArithmeticException if numeric overflow occurs
   */
  @Override  // override for Javadoc and performance
  default int get(TemporalField field) {
    if (field == ERA) {
      return getValue();
    }
    return TemporalAccessor.super.get(field);
  }

  /**
   * Gets the value of the specified field from this era as a {@code long}.
   * <p>
   * This queries this era for the value of the specified field.
   * If it is not possible to return the value, because the field is not supported
   * or for some other reason, an exception is thrown.
   * <p>
   * If the field is a {@link ChronoField} then the query is implemented here.
   * The {@code ERA} field returns the value of the era.
   * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
   * <p>
   * If the field is not a {@code ChronoField}, then the result of this method
   * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
   * passing {@code this} as the argument. Whether the value can be obtained,
   * and what the value represents, is determined by the field.
   *
   * @param field the field to get, not null
   * @return the value for the field
   * @throws DateTimeException if a value for the field cannot be obtained
   * @throws UnsupportedTemporalTypeException if the field is not supported
   * @throws ArithmeticException if numeric overflow occurs
   */
  @Override
  default long getLong(TemporalField field) {
    if (field == ERA) {
      return getValue();
    } else if (field instanceof ChronoField) {
      throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
    }
    return field.getFrom(this);
  }

  //-----------------------------------------------------------------------

  /**
   * Queries this era using the specified query.
   * <p>
   * This queries this era using the specified query strategy object.
   * The {@code TemporalQuery} object defines the logic to be used to
   * obtain the result. Read the documentation of the query to understand
   * what the result of this method will be.
   * <p>
   * The result of this method is obtained by invoking the
   * {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
   * specified query passing {@code this} as the argument.
   *
   * @param <R> the type of the result
   * @param query the query to invoke, not null
   * @return the query result, null may be returned (defined by the query)
   * @throws DateTimeException if unable to query (defined by the query)
   * @throws ArithmeticException if numeric overflow occurs (defined by the query)
   */
  @SuppressWarnings("unchecked")
  @Override
  default <R> R query(TemporalQuery<R> query) {
    if (query == TemporalQueries.precision()) {
      return (R) ERAS;
    }
    return TemporalAccessor.super.query(query);
  }

  /**
   * Adjusts the specified temporal object to have the same era as this object.
   * <p>
   * This returns a temporal object of the same observable type as the input
   * with the era changed to be the same as this.
   * <p>
   * The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
   * passing {@link ChronoField#ERA} as the field.
   * <p>
   * In most cases, it is clearer to reverse the calling pattern by using
   * {@link Temporal#with(TemporalAdjuster)}:
   * <pre>
   *   // these two lines are equivalent, but the second approach is recommended
   *   temporal = thisEra.adjustInto(temporal);
   *   temporal = temporal.with(thisEra);
   * </pre>
   * <p>
   * This instance is immutable and unaffected by this method call.
   *
   * @param temporal the target object to be adjusted, not null
   * @return the adjusted object, not null
   * @throws DateTimeException if unable to make the adjustment
   * @throws ArithmeticException if numeric overflow occurs
   */
  @Override
  default Temporal adjustInto(Temporal temporal) {
    return temporal.with(ERA, getValue());
  }

  //-----------------------------------------------------------------------

  /**
   * Gets the textual representation of this era.
   * <p>
   * This returns the textual name used to identify the era,
   * suitable for presentation to the user.
   * The parameters control the style of the returned text and the locale.
   * <p>
   * If no textual mapping is found then the {@link #getValue() numeric value} is returned.
   * <p>
   * This default implementation is suitable for all implementations.
   *
   * @param style the style of the text required, not null
   * @param locale the locale to use, not null
   * @return the text value of the era, not null
   */
  default String getDisplayName(TextStyle style, Locale locale) {
    return new DateTimeFormatterBuilder().appendText(ERA, style).toFormatter(locale).format(this);
  }

  // NOTE: methods to convert year-of-era/proleptic-year cannot be here as they may depend on month/day (Japanese)
}
